Dynamically updating factbox

I'm trying to dynamically update fields a new factbox that I've added to the sales order page. The factbox essentially contains statistics of the sales order (e.g. number of items, total amount of sales order, etc.)

I'd like to have this refreshed as sales lines are updated. For example, as the user enters a sales line quantity, the aggregate item quantities are updated in the factbox.

The sales line factbox works in a similar fashion at the line level, updating for example the Availability field, but I haven't found the mechanism that refreshes it.

Thanks in advance.